1. Field of the Invention
The present invention relates to a method of producing a sheet metal gear, and more particularly to a sheet-metal gear production method in which a flat metal sheet is used as a starting material from which can be produced easily and accurately, not only gears of a small diameter but also gears of a relatively large diameter, such as a drive plate or a timing pulley used as a starter part of an automobile.
2. Description of the Prior Art
A prior art method of producing a ring-like gear such as a drive plate for an automobile using a flat sheet metal as a starting material is disclosed in Japanese Laid-Open Patent Publication No. 6-63670.
FIGS. 10 to 14 illustratively show the production method disclosed in this Japanese Patent Publication.
In the production method, a flat circular metal sheet 1 shown in FIG. 10 is used as a starting material. In an initial step, as shown in FIG. 11, an operation is performed in which the circular metal sheet 1 attached to a rotary die 101 is pressed radially inwardly by a die 102. As a result of this step, a cylindrical side plate portion 11 is formed by bending the outer periphery of the metal sheet 1. In the next step, as shown in FIG. 12, a two-layered bulge portion 12 is formed into a ring like shape in the base of the side plate portion 11 of the metal sheet 1 by the action of upper and lower pressing dies 103 and 104. In a further succeeding step shown in FIG. 13, an operation is conducted in which the bulge portion 12 is radially inwardly pressed by a die 105. As a result of this step, the bulge portion 12 (see FIG. 11) is thickened for formation as a gear portion 13.
After the thickened gear portion 13 is formed in the metal sheet 1 as described above, a step of shaping peaks and valleys in the gear portion 13 is conducted. In this step, as shown in FIG. 14, a shaping roller 106 is used. The shaping roller has a projecting valley-shaping face 107, and a recessed peak-shaping face 108. In this step, the shaping roller 106 and the metal sheet 1 are synchronously rotated while pressing the shaping roller 106 against the gear portion 13 (see FIG. 14) of the metal sheet 1. As a result of conducting this step, the places of the gear portion 13 of the metal sheet 1 with which the valley-shaping face 107 collides are recessed to be formed into valleys of a gear, and the places corresponding to the peak-shaping face 108 are projected to be formed into peaks of the gear.
In the prior art production method shown in FIGS. 10 to 14, the gear portion 13 has a flat peripheral face which is pressed by the valley-shaping face 107 and the peak-shaping face 108 of the shaping roller 106 in the initial stage of the step of shaping peaks and valleys in the gear portion 13 of the metal sheet 1. The pressing against the gear portion 13 having the flat peripheral face causes infant recesses of the valleys of the gear and infant projections of the peaks to be formed. Thereafter, the depth of each recessed place is gradually increased, and the height of each projected peak is gradually increased. Finally, valleys of an adequate depth and peaks of an adequate height are shaped.
In the production method, it is requested that the shaping roller 106 which is coupled to a rotation transmission mechanism, and the gear portion 13 of the metal sheet 1 are correctly synchronously rotated so that there never occurs slippage between the roller and the gear portion, because, when slippage between the two members occurs, the valleys and peaks of the gear cannot be shaped with correct pitches. Therefore, an accurate rotation transmission mechanism which can correctly synchronize rotation of the metal sheet 1 with that of the shaping roller 106 is required. This causes the cost of the production facility to be increased.
In the production method, the whole of the depth of each valley and that of the height of each peak of a gear are formed by rotating the shaping roller 106 and the metal sheet in specific directions while pressing the shaping roller 106 against the gear portion 13. Consequently, valleys and peaks of a resulting gear tend to have uneven thickness. In order to prevent such uneven thickness from occurring, it is effective to proceed with the shaping operation while repeatedly alternating the rotation directions of the metal sheet 1 and the shaping roller 106. However, this countermeasure complicates the production process. cl SUMMARY OF THE INVENTION
It is an object of the present invention to finish easily and accurately pitches of valleys and peaks of a gear while employing a simple production facility and an uncomplicated production process.
It is another object of the present invention to remarkably shorten the time period required for completing the formation of a gear in the outer peripheral edge of a flat metal sheet, as compared with the prior art described above, thereby greatly enhancing productivity.
It is a further object of the present invention to economically produce a metal sheet gear by using a low cost production facility.
In order to attain these objects, the method of producing a sheet metal gear according to the present invention comprises: a preparation step of punching out a number of places at an outer peripheral edge of a metal sheet in an axial direction of the metal sheet, the places being arranged with a regular pitch, thereby forming preliminary valleys for the gear and preliminary peaks respectively existing between adjacent ones of the preliminary valleys; and
a gear forming step of fitting a valley-shaping face of a shaping roller having a peak-shaping face and the valley-shaping face into the preliminary valleys, and the peak-shaping face of the shaping roller onto the preliminary peaks, and rotating the shaping roller while following the metal sheet and pressing the shaping roller against the metal sheet, thereby increasing the depth of the preliminary valleys of the metal sheet to form shaped valleys of the gear, and increasing the height of the preliminary peaks to form shaped peaks of the gear. PA1 a gear finishing step of fitting a valley-shaping face of a shaping roller having a peak-shaping face and the valley-shaping face into the valleys of the metal sheet, and the peak-shaping face of the shaping roller onto the peaks of the metal sheet, and rotating the shaping roller while following the metal sheet, thereby finishing surfaces of the valleys and the peaks of the metal sheet.
According to the production method, a roller which can rotate while following a metal sheet can be used as the shaping roller. Therefore, an accurate rotation transmission mechanism which is used in a conventional production facility and is used for synchronously rotating a metal sheet and a shaping roller is not required. This enables a simple and economical production facility to be used.
At a stage in which the preparation step of punching out the outer peripheral edge of a metal sheet to form preliminary valleys and peaks for a gear has been conducted, the correct pitches of the valleys and peaks of the gear for the final shaped product are determined. In the gear forming step, therefore, the preliminary valleys are accurately shaped into valleys of final shape, the preliminary peaks are accurately shaped into peaks of final shape, and the pitches of the peaks and valleys of the final shape are accurately formed, only by fitting the valley-shaping face of the shaping roller into the preliminary valleys, and the peak-shaping face of the shaping roller onto the preliminary peaks, and rotating the shaping roller while following the metal sheet and pressing the metal shaping roller against the metal sheet, i.e., by rotating the shaping roller together with the metal sheet.
In the production method, the procedure of increasing the depth of the preliminary valleys, which are previously formed by punching, and the height of the preliminary peaks, which are previously formed between adjacent ones of the preliminary valleys is carried out. As compared with the prior art method in which the entire valleys and peaks are formed by using a shaping roller as described above, therefore, the time period required for forming a gear in the outer peripheral edge of a metal sheet can be shortened, and the shortened time period enhances productivity.
The method of producing a sheet metal gear according to another aspect of the present invention comprises: a punching step of punching out a number of places of an outer peripheral edge of a metal sheet in an axial direction of the metal sheet, the places being arranged with a regular pitch, thereby forming valleys of the gear and peaks respectively existing between adjacent ones of the valleys; and
In the production method, the shaping roller is not used for increasing the depth of valleys and the height of peaks. In other words, the shaping roller used in the method is required only to serve to finish the surfaces of valleys and peaks of a metal sheet. In the production method, therefore, it is not necessary to carry out the above-mentioned procedure, i.e., the procedure of increasing the depth of the preliminary valleys and the height of the preliminary peaks by a shaping roller, and hence the time period for executing the procedure can be saved. This serves to remarkably shorten the time period required for forming a gear in the outer peripheral edge of a metal sheet, and also to greatly enhance the productivity.
When either of the two production methods described above is employed, it is effective to use a metal sheet having a thickness which is equal to that of the peaks of a gear to be shaped. Alternatively, a metal sheet having a thickness which is smaller than that of the peaks of a gear to be shaped may be used. In the case where a metal sheet having a thickness which is smaller than that of the peaks of a gear to be shaped is used, it is preferable to thicken the outer peripheral edge of the metal sheet before the preparation step or the punching step. When a method in which a metal sheet having a thickness which is smaller than that of the peaks of a gear to be shaped is used is employed, the weight and cost of a metal sheet used as the starting material can be reduced. This produces an advantage in that the reduction serves to suppress the material cost to a low level.